As the image recording apparatus, a photo printer is known, which records an image on a photosensitive recording material or called photographic paper by exposing it to light obtained from an image photographed on negative film. As for such photo printers, the mainstream was a direct exposure style that exposes the photosensitive recording material to an optical image projected from the negative film onto the photosensitive material. However, digital photo printers have been put into practical use, which capture the image on the negative film as image data by photoelectric conversion, perform various image processing to the image data and exposes the photosensitive material to recording light modulated according to the image.
Most of the digital photo printers cut a long web of photosensitive material into a given length according to the designated size of photo prints, and expose the cut sheet of photosensitive material to record the image. If, however, a leading edge of the photosensitive material is on the skew relative to a main scan direction of an exposure section or an image recording device when exposing the cut sheet of photosensitive material to record the image, the image is recorded on the skew. For this reason, it is necessary to correct the skew of the photosensitive material and supply the photosensitive material to the exposure section in an appropriate position with no skew.
In order to solve such problem, the skew of the photosensitive material is conventionally corrected before supplying the cut sheets of photosensitive material to the exposure section. For example, a sheet conveyer device with a skew correcting device is known from Japanese Laid-open Patent Application No. 2003-292198. The skew correction device consists of a roller pair whose one end is a bearing section and whose other end is movable up and down in a direction perpendicular to the paper path. The sheet conveyer device corrects the skew of the photosensitive material by moving one end of the roller pair so as to provide a difference in length of the paper path between opposite ends of the paper path in a widthwise direction of the paper path, that is equivalent to the main scan direction.
In order to detect the skew of the photosensitive material, the sheet conveyer device described in the above-mentioned prior art apposes two detecting sensors along the widthwise direction of the paper path to detect each leading edge of the photosensitive material. Based on which of these two sensors detects the leading edge first and how much the difference in detection time between the two sensors, the direction and angle of inclination of the leading edges relative to the main scan direction, hereinafter collectively referred to as the skew of the leading edge, is determined. However, according to this prior art, a minute change in transport speed or a deviation in mounting position of the detecting sensors will cause a detection error, so it is difficult to accurately detect the skew based on the outputs of these detecting sensors. Moreover, because the skew correcting device itself involves some tolerance as a unit, it is impossible to feedback-control the tolerance of the skew correcting device based on the outputs of the detecting sensors. For this reason, it has been hard to correct the skew of the photosensitive material with high accuracy enough to obtain high quality photo prints.